Since the early 1980s, thousands of patients prone to irregular and sometimes life-threatening heart rhythms have had miniature heart monitors, particularly defibrillators and cardioverters, implanted in their bodies, typically in the upper chest area above their hearts. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current to the heart. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives.
The typical defibrillator or cardioverter includes a set of electrical leads, which extend from a sealed housing into the wall of a heart after implantation. Within the housing are a battery for supplying power, monitoring circuitry for detecting abnormal heart rhythms, and a capacitor for delivering bursts of electric current through the leads to the heart.
The capacitor can take the form of a flat aluminum electrolytic capacitor. Flat capacitors include a stack of flat capacitor elements mounted within a capacitor case. Each flat capacitor element includes one or more separators between two sheets of aluminum foil. One of the aluminum foils serves as a cathode (negative) foil, and the other serves as an anode (positive) foil. Sometimes, two or more foils are stacked one on the other to form a multi-anode stack. The capacitor elements each have an individual capacitance (or energy-storage capacity) proportional to the surface area of the aluminum foil.
One drawback with these capacitors is that they consume significant space within the implantable defibrillators and cardioverters and thus limit how small these devices can be made. However, the size of the capacitor cannot be arbitrarily reduced without reducing the capacitance of the device. Accordingly, there is a need to reduce the size of the capacitor while also maintaining or increasing its capacitance. Further, there is a need to provide a compact capacitor capable of providing the required pulse of energy for use within the device and to provide for a design efficiently utilizing space within the capacitor case.